ac/nir: Enable nir_opt_large_constants

ac/nir: Enable nir_opt_large_constants

vkpipeline-db numbers:

Totals:
SGPRS: 1740306 -> 1741322 (0.06 %)
VGPRS: 1331124 -> 1331712 (0.04 %)
Spilled SGPRs: 21201 -> 21316 (0.54 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 256 -> 256 (0.00 %) dwords per thread
Code Size: 79022628 -> 78694788 (-0.41 %) bytes
LDS: 6500 -> 6500 (0.00 %) blocks
Max Waves: 301413 -> 301302 (-0.04 %)
Wait states: 0 -> 0 (0.00 %)

Totals from affected shaders:
SGPRS: 53633 -> 54649 (1.89 %)
VGPRS: 53000 -> 53588 (1.11 %)
Spilled SGPRs: 3454 -> 3569 (3.33 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 5284232 -> 4956392 (-6.20 %) bytes
LDS: 2 -> 2 (0.00 %) blocks
Max Waves: 4239 -> 4128 (-2.62 %)
Wait states: 0 -> 0 (0.00 %)

(The biggest VGPR and max wave regression is due to unrolling a loop,
which made the scheduler more aggressive, but in this case it's able to
effectively hide latency so it's actually probably a win.)

shader-db numbers with radeonsi NIR:

Totals:
SGPRS: 3526496 -> 3526512 (0.00 %)
VGPRS: 2198576 -> 2198576 (0.00 %)
Spilled SGPRs: 10463 -> 10463 (0.00 %)
Spilled VGPRs: 86 -> 86 (0.00 %)
Private memory VGPRs: 3182 -> 2528 (-20.55 %)
Scratch size: 3308 -> 2640 (-20.19 %) dwords per thread
Code Size: 74117280 -> 74106140 (-0.02 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 775846 -> 775844 (-0.00 %)
Wait states: 0 -> 0 (0.00 %)

Totals from affected shaders:
SGPRS: 856 -> 872 (1.87 %)
VGPRS: 680 -> 680 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 654 -> 0 (-100.00 %)
Scratch size: 668 -> 0 (-100.00 %) dwords per thread
Code Size: 49652 -> 38512 (-22.44 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 182 -> 180 (-1.10 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Marek Olšák <marek.olsak@amd.com>